Fan assembly and method

ABSTRACT

The axial fan assembly according to some embodiments of the present invention has a shroud, a motor coupled to the shroud, and a fan coupled to the motor. By employing selected vane-to-blade ratios, blade twist angles, blade pitch angles, blade-to-shroud axial gaps, shroud solidities, vane swept angles, and vane inlet and outlet angles of specified amounts or falling within specified ranges, desirable fan performance is achieved. Any one or more of these parameters can be utilized alone or in combination with other parameters as desired.

BACKGROUND OF THE INVENTION

Fans are used to generate air movement in a wide variety ofapplications, such as in heating, ventilating, and cooling systems. Forexample, a variety of axial-type fans (i.e., fans in which fluid ismoved in a direction along the axis of rotation of the fan) are used inmany industrial applications such as for ventilation purposes in officebuildings, greenhouses, barns, factories, and other structures. Axialventilation fans also have residential uses, such as in kitchens andbathrooms. As previously mentioned, axial fans are also commonly used inheating and cooling systems for heat transfer purposes. For example,axial fans are used for heat transfer purposes in a variety ofapplications, such as in air conditioning units, refrigeration units,computers, and in cars and other vehicles. In most of theseapplications, the fan is used to move air across a heat exchanger,wherein heat is transferred to the air as it passes by and/or throughthe heat exchanger.

Fan efficiency has become increasingly important, regardless of the typeor application of the fan. Fan efficiency is typically important becausefans are commonly driven by electric motors or other driving devicesthat consume valuable power. Inefficient fans consume more power, andare therefore less desirable than more efficient fans. Also, inefficientfans tend to require a different rotor geometry than efficient fans inorder to meet the ventilation and heat transfer requirements of thesystems in which the fans are used. For example, if a certain air flowis necessary for a system, an inefficient fan may have a greater numberof blades, a greater diameter, and/or a larger motor than a moreefficient fan. Therefore, inefficient fans can cost more than efficientfans in terms of materials and manufacturing expenses, and can occupyvaluable system space. As such, fan manufacturers continue to search forways to increase the efficiency of axial fans.

The marketplace, however, often places contradictory constraints uponfan manufacturers. For example, users of axial fans typically desire arelatively high fan efficiency, but also want fans that are compact andthat generate the least noise possible. These constraints are oftencontradictory because many believe that fans generally need to be largerin order to reduce fan noise and/or airflow. Thus, in some cases, onedemand can be met at the expense of another.

Axial fan efficiency is affected by a number of factors. For example,the efficiency of the motor or other device driving an axial fan can bean important factor in the overall efficiency of a axial fan and motorassembly. As another example, the speed of the fan motor and blades canimpact fan efficiency. Increased fan motor and blade speed generallyincreases the amount of air turbulence moving through the fan—a resultthat is normally detrimental to fan efficiency. Turbulence is also aprimary factor influencing the noise level of a fan.

The design and orientation of axial fan blades (e.g., axial fan bladeshape, orientation with respect to the rest of the fan, and the like)are also factors in axial fan efficiency. It is generally recognizedthat certain shapes of fan blades are more efficient than others. Forexample, a machete or teardrop-shaped blade can often be more efficientthat a cloverleaf-shaped blade.

The clearance between the blades of a fan and the fan housing can alsoimpact axial fan efficiency. In many cases, this clearance is thedistance between the tips of rotating blades and an adjacent fan housingwall. Blade-to-housing clearance is typically important because it oftenhas a direct bearing upon the static pressure capabilities of the fan.For example, larger clearances between fan blade tips and adjacenthousing walls can result in lower static pressure capabilities and lowerfan efficiencies.

The design of an axial fan housing also impacts the efficiency of theaxial fan. For example, the design of an fan housing air inlet cansignificantly influence efficiency of the axial fan by impacting theamount of turbulence within the fan. Turbulence within an axial fan cancreate a phenomenon known as vena contracta, which results in thereduction of the effective cross sectional area of the air inlet. Such areduction permits less air to move through the air inlet, therebyreducing the efficiency of the axial fan.

Many of the efficiency factors discussed above are taken into accountwhen designing conventional axial fans. However, still other efficiencyfactors can be important to axial fan performance, some of which areoften not considered in conventional axial fan designs. Higherefficiency axial fans would be a welcome addition to the art.

SUMMARY OF THE INVENTION

Some embodiments of the present invention provide a fan assemblycomprising a motor; a fan rotatably coupled to the motor for rotationabout an axis and having a plurality of fan blades each having a leadingedge with respect to a rotational direction of the fan blade and atrailing edge with respect to the rotational direction of the fan blade;and a shroud including a plurality of vanes extending transversely withrespect to fluid flow through the fan assembly and through which fluidflows through the fan assembly, wherein the vanes are located downstreamof the fan and oriented to extend away from a central area of theshroud, wherein each vane has a length defined between a radially innerend of the vane and a radially outer end of the vane, a leading edge, atrailing edge downstream of the leading edge of the vane with respect tofluid flow through the fan assembly, and a rearward swept angle definedbetween a first straight line extending through the radially inner andouter ends of the vane and a second straight line extending from theaxis of the fan to the radially inner end of the vane, wherein therearward swept angle is no less than about 5 degrees and is no greaterthan about 45 degrees, wherein each of the vanes is spaced from anadjacent vane by a gap measured from a first point on a first vane to acorresponding point on an adjacent vane, wherein each vane also has achord length at the first point measured from the vane leading edge tothe vane trailing edge, and wherein the fan assembly has a ratio ofchord length to vane gap of no less than about 0.2 and no greater thanabout 3.5.

Also, some embodiments of the present invention provide a fan assemblycomprising a motor; a fan rotatably coupled to the motor for rotationabout an axis, wherein the fan has a plurality of fan blades each havinga leading edge with respect to a rotational direction of the fan bladeand a trailing edge with respect to the rotational direction of the fanblade; and a shroud including a plurality of vanes extendingtransversely with respect to fluid flow through the fan assembly andthrough which fluid flows through the fan assembly, wherein the vanesare located downstream of the fan and oriented to extend away from acentral area of the shroud, wherein each vane has a length definedbetween a radially inner end of the vane and a radially outer end of thevane, a leading edge, a trailing edge downstream of the leading edge ofthe vane with respect to fluid flow through the fan assembly, and aninlet angle defined between a straight line tangent to the vane at theleading edge of the vane and a plane orthogonal to the axis of the fan,wherein the straight line lies in a plane tangent to an imaginarycylinder centered at the axis of the fan, wherein the inlet angle is noless than about 20 degrees and is no greater than about 70 degrees,wherein each of the vanes is spaced from an adjacent vane by a gapmeasured from a first point on a first vane to a corresponding point onan adjacent vane, wherein each vane also has a chord length at the firstpoint measured from the vane leading edge to the vane trailing edge, andwherein the fan assembly has a ratio of chord length to vane gap of noless than about 0.2 and no greater than about 3.5.

In some embodiments, a fan assembly is provided, and comprises a motor;a fan rotatably coupled to the motor for rotation about an axis, whereinthe fan has a plurality of fan blades each having a leading edge withrespect to a rotational direction of the fan blade and a trailing edgewith respect to the rotational direction of the fan blade; and a shroudincluding a plurality of vanes extending transversely with respect tofluid flow through the fan assembly and through which fluid flowsthrough the fan assembly, wherein the vanes are located downstream ofthe fan and oriented to extend away from a central area of the shroud,wherein each vane has a length defined between a radially inner end ofthe vane and a radially outer end of the vane, a leading edge, atrailing edge downstream of the leading edge of the vane with respect tofluid flow through the fan assembly, and an outlet angle defined betweena straight line tangent to the vane at the trailing edge of the vane anda line parallel to the axis of the fan, wherein the straight line liesin a plane tangent to an imaginary cylinder centered at the axis of thefan, wherein the outlet angle is no less than about 30 degrees in adirection counter to rotation of the fan and is no greater than about 30degrees in a rotational direction of the fan; wherein each of the vanesis spaced from an adjacent vane by a gap measured from a first point ona first vane to a corresponding point on an adjacent vane, wherein eachvane also has a chord length at the first point measured from the vaneleading edge to the vane trailing edge, and wherein the fan assembly hasa ratio of chord length to vane gap of no less than about 0.2 and nogreater than about 3.5.

Some embodiments of the present invention provide a fan assembly,comprising a motor; a fan rotatably coupled to the motor for rotationabout an axis, wherein the fan has a plurality of fan blades each havinga leading edge with respect to a rotational direction of the fan bladeand a trailing edge with respect to the rotational direction of the fanblade; and a shroud including a plurality of vanes extendingtransversely with respect to fluid flow through the fan assembly andthrough which fluid flows through the fan assembly, wherein the vanesare located downstream of the fan and oriented to extend away from acentral area of the shroud, wherein each vane has a length definedbetween a radially inner end of the vane and a radially outer end of thevane, a leading edge, and a trailing edge downstream of the leading edgeof the vane with respect to fluid flow through the fan assembly, whereinthe shroud is separated from the fan by an axial gap between the leadingedges of the vanes and the trailing edges of the fan blades, wherein thegap is no less than about 0.15 inches and no greater than about 1.5inches, wherein each of the vanes is spaced from an adjacent vane by agap measured from a first point on a first vane to a corresponding pointon an adjacent vane, wherein each vane also having a chord length at thefirst point measured from the vane leading edge to the vane trailingedge, and wherein the fan assembly also has a ratio of chord length tovane gap of no less than about 0.2 and no greater than about 3.5.

In additional embodiments of the present invention, a fan assembly isprovided, and comprises a motor; a fan rotatably coupled to the motorfor rotation about an axis, wherein the fan has a plurality of fanblades each having a leading edge with respect to a rotational directionof the fan blade and a trailing edge with respect to the rotationaldirection of the fan blade; and a shroud including a plurality of vanesextending transversely with respect to fluid flow through the fanassembly and through which fluid flows through the fan assembly, whereinthe vanes are located downstream of the fan and oriented to extend awayfrom a central area of the shroud, wherein each vane has a leading edgeand a trailing edge downstream of the leading edge with respect to fluidflow through the fan assembly, wherein each of the vanes is spaced froman adjacent vane by a gap measured from a first point on a first vane toa corresponding point on an adjacent vane, wherein each vane also has achord length at the first point measured from the vane leading edge tothe vane trailing edge, and wherein the fan assembly has a ratio ofchord length to vane gap of no less than about 0.2 and no greater thanabout 2.5.

Further objects and advantages of the present invention, together withthe organization and operation thereof, will become apparent from thefollowing detailed description of the invention when taken inconjunction with the accompanying drawings, wherein like elements havelike numerals throughout the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is further described with reference to theaccompanying drawings, which show an exemplary embodiment of the presentinvention. However, it should be noted that the invention as disclosedin the accompanying drawings is illustrated by way of example only. Thevarious elements and combinations of elements described below andillustrated in the drawings can be arranged and organized differently toresult in embodiments which are still within the spirit and scope of thepresent invention.

In the drawings, wherein like reference numeral indicate like parts:

FIG. 1A is a cross-sectioned elevational view of a fan assembly of thepresent invention, shown mounted near a heat exchanger;

FIG. 1B is a cross-sectioned elevational view of the fan assembly of thepresent invention illustrated in FIG. 1A, shown mounted in an alternateconfiguration;

FIG. 2 is an exploded view of the fan assembly illustrated in FIGS. 1Aand 1B;

FIG. 3 is a perspective view of the fan assembly illustrated in FIGS.1A, 1B, and 2, shown partially sectioned;

FIG. 4 is a plan view of the fan assembly illustrated in FIGS. 1A, 1B, 2and 3, viewed from the shroud side of the fan assembly;

FIG. 5 is a side cross-sectional view of the fan assembly illustrated inFIGS. 1-4, taken along lines 5—5 of FIG. 4;

FIG. 6 is a plan view of the fan assembly illustrated in FIGS. 1-5,viewed from the fan side of the assembly;

FIG. 7 is a detail cross-sectional side view of part of the fan assemblyillustrated in FIGS. 1-6, taken along lines 7—7 of FIG. 4;

FIG. 8 is an enlarged view of the cross-sectioned elements illustratedin FIG. 7;

FIG. 9 is an end view of a fan blade from the fan assembly illustratedin FIGS. 1-8; and

FIGS. 10A-10C are performance curve comparison charts showing theperformance of the fan assembly illustrated in FIGS. 1-9 compared to twoconventional axial fans.

DETAILED DESCRIPTION OF EMBODIMENTS

An exemplary embodiment of an axial flow fan assembly 10 according tothe present invention is illustrated in FIGS. 1-10. The exemplary fanassembly 10 in FIGS. 1-10 has a shroud 14, a motor 42 coupled to theshroud 14, and a fan 50 coupled to the motor 42. In operation, the motor42 rotates a drive shaft 46 coupled to the fan 50. As the drive shaft 46rotates, it powers the fan 50 to rotate within the shroud 14, andgenerates air movement. FIGS. 1A and 1B illustrate the fan in anexemplary environment. As illustrated, the fan is mounted to generate astream of air to remove heat from condensing coils. This is just one ofthe many possible uses of this fan. Although a heat exchange environmentis described herein and illustrated in FIGS. 1A and 1B, the fan of thepresent invention can be employed in any air moving application. Otheruses known by those having ordinary skill in the art fall within thespirit and scope of the present invention.

As illustrated in FIGS. 2-6, the illustrated shroud 14 at leastpartially encloses fan blades 58 extending from a hub 54 of the fan 50.A portion of the shroud 14 has a generally circular wall 17 that extendsaround the radial periphery of the fan 50, although shrouds having anyother wall shape can instead be employed as desired. The generallycircular shaped wall 17 illustrated in FIGS. 2-6 (often referred to as afan cylinder or fan ring) can have any diameter desired, depending atleast in part upon the size of the fan employed. In some embodiments,the fan assembly has a nominal size between six inches and eighteeninches. However, other sized fans also fall within the spirit and scopeof the present invention.

The fan shroud 14 in the illustrated exemplary embodiment has a set ofmounting bosses 15 that can be employed to mount the fan assembly 10 toa frame, housing, or other structure. Any number of mounting bosseshaving any shape can be employed, such as tab-shaped protrusionsextending from the wall 17 of the shroud 14 as shown in the figures,lugs, posts, or fingers extending from the wall 17, a rib or flangeextending partially or fully around the wall 17, and the like. Suchmounting elements or features can be secured to a frame, housing, orother structure by bolts, screws, nails, rivets, pins, or otherconventional fasteners, by clamps, clips, inter-engaging or snap-fitfingers or other features, and the like.

In some embodiments, the same fan assembly 10 can be mounted indifferent orientations as needed in different applications. For example,it may be desirable to mount the fan assembly 10 in one orientation inorder to pull air through a condenser or other device, while in anotherapplication is may be desirable to mount the fan in a reversed directionto blow air into a condenser or other device. This mounting versatilityis provided in some embodiments by the use of two different shrouds 14,each of which has mounting elements or features (described above)located at different axial positions on the shroud 14. In theillustrated embodiment for example, one shroud 14 has mounting bosses 15located at a downstream end of the fan assembly 10 (see FIG. 1A), whileanother shroud 14′ has mounting bosses 15′ located at an upstream end ofthe fan assembly 10 (see FIG. 1B). In this manner, a shroud 14, 14′ canbe selected that will enable at least the majority of the fan assembly10 to be recessed within the structure to which it is mounted.

In other embodiments, the mounting elements or features of the shroud 14can be located in any axial position along the shroud 14. By way ofexample only, mounting bosses 15 can be located at an axial mid-pointbetween the ends of the shroud 14, thereby permitting the fan assembly10 to be mounted in both orientations described above without the needfor two different shrouds and while still keeping a substantial portionof the fan assembly 10 recessed within the structure to which it ismounted in both orientations. Regardless of the axial location of themounting elements or features employed on the shroud 14, the fanassembly 10 can still be mounted in two opposite orientations (althoughthe ability to recess a majority or the entirety of the fan assembly 10in both orientations may be limited).

The mounting elements or features 15 of the shroud 14 described abovecan be integral with the shroud 14. However, in other embodiments thesemounting elements or features 15 are attached to the shroud 14 in anysuitable manner, such as by a ring (not shown) encircling the shroud 14and that can be secured with respect to the shroud 14 in a number ofdifferent axial positions. As another example, the mounting elements orfeatures 15 can be attached to the shroud 14 at different axiallocations by screws, bolts, nails, rivets, pins, or other conventionalfasteners, inter-engaging elements, adhesive or cohesive bondingmaterial, and the like.

The size of the fan ring 17 with respect to the fan 50 can have animpact on the efficiency of the fan assembly 10. As will be described ingreater detail below, the efficiency of the fan assembly 10 can increaseas the spacing between the fan 50 and the fan ring 17 decreases. Thus,in some embodiments of the present invention, the fan ring 17 generallyhas an inside diameter nearly matching the outside diameter of the fan50. More specifically, in some embodiments good performance results areachieved by using a fan ring 17 having an inside diameter providing anon-contacting clearance fit with the fan blades 58 or a clearance notexceeding 0.125 inches. A clearance between the fan blades 58 and thefan ring 17 of no greater than 0.08 can provide better performanceresults. Also, a clearance between the fan blades 58 and the fan ring 17not exceeding 0.05 inches can provide still better performance results.

As seen in FIG. 3, the fan cylinder 17 can have a double wall. Althougha single-walled fan cylinder 17 can be employed, a double wall fancylinder can reduce vibration generated by operation of the fan assembly10.

The shroud 14 in the illustrated exemplary embodiment has a plurality ofvanes 18 directly or indirectly attached to the fan cylinder 17 at oneend of the fan cylinder 17. Although the vanes 18 can be integral withthe fan cylinder 17 as shown in FIGS. 2-5, in other embodiments thevanes 18 are not integral with the cylinder 17, and can be attached tothe cylinder in any conventional manner. Furthermore, even though thevanes 18 of the illustrated embodiment are located at one end or at theedge of the cylinder 17, the vanes 18 do not necessarily need to belocated at an end or edge of the cylinder 17. For example, dependingupon the shape and length of the fan cylinder 17, the vanes 18 could belocated in different axial positions along the fan cylinder 17. Theplurality of vanes 18 can serve several functions. For example, thevanes 18 can do one or more of the following: help to increaseperformance of the fan assembly 10, alter the direction of air movementthrough the fan assembly 10, and/or act as a safety device (to limit orprevent access to the fan 50 through the shroud 14). As shown in theillustrated embodiment, the vanes 18 can extend in generally radialdirections from the fan cylinder 17 towards the center of the shroud 14.The vanes 18, however, do not necessarily have to extend directlyradially. Rather, in alternative embodiments, the vanes 18 can have anyorientation with respect to the shroud 14, including but not limited toorientations in which the vanes 18 are parallel to radial linesextending from an axis of rotation of the fan 50, orientations in whichthe vanes are at an angle with respect to such radial lines (e.g.,wherein the radially innermost portion of each vane 18 is located infront of or behind the radially outermost portion of each vane 18 in thecircumferential direction), orientations in which imaginary lines drawnthrough the length of the vanes 18 intersect an axis of rotation of thefan 50, orientations in which such imaginary lines do not intersect theaxis of rotation of the fan 50, and the like.

The vanes 18 of the shroud 14 can be arranged on the shroud 14 in anydesired manner. By way of example only, the vanes 18 can be equallyspaced from one another, can be arranged in any pattern desired (i.e.,repeating or non-repeating pattern), or can be randomly spaced. In theillustrated exemplary embodiment, the vanes 18 extend in a generallyradial direction and are also angled with respect to the direction offan rotation. More specifically, the radially innermost end of each vane18 illustrated in the figures is located circumferentially ahead of theradially outermost end of the vane 18 (with reference to the directionof rotation of the fan 50). As explained above, the vanes 18 can insteadbe oriented in an opposite direction, in which case the radiallyinnermost end of each vane 18 is located circumferentially behind theradially outermost end of the vane 18.

If employed, vanes 18 can be located on all or any portion of the shroud14, including the fan cylinder 17. As shown in the illustratedembodiment, vanes 18 cover the majority of the shroud 14 surfaceperpendicular to the axis of rotation of the fan 50. However, asillustrated, the vanes 18 extend only partially between the fan cylinder17 and the center of the fan cylinder 17. In the illustrated embodimentof the present invention, vanes 18 extend across the same general areain front of the fan 50 (downstream of the fan 50) as the fan blades 58.The remainder of the center portion of the shroud 14, as seen in FIGS. 2and 3, can serve to house the motor 42 as shown in the figures.Therefore, in some embodiments of the present invention, vanes 18 arenot included in this area of the shroud 14. However, in someembodiments, vanes 18 can be placed in this area, depending at least inpart upon the axial position of the motor 42 with respect to the shroud14.

Regardless of the number and orientation of the vanes 18, the vanes 18can take any cross-sectional shape desired. For example, each vane 18can be flat, triangular, U-shaped, can have a generally airfoil shape,can present a concave or convex shape toward or away from the directionof rotation of the blades 58 and/or in either direction along the axisof rotation of the fan 50, and the like. Furthermore, the vanes 18 canbe cambered between the vane leading edges 30 and vane trailing edges 34and/or can be twisted along the length of the vanes (in a clockwise orcounterclockwise direction viewed along the length of the blade from tipto root), or the like. As best illustrated in FIG. 8, vanes 18 of theillustrated embodiments have a cambered, generally airfoil-likecross-section, wherein the concave portion of the cambered vanes 18faces the leading edge of the blades 58. In addition, the vanes 18 canhave any shape desired along the length of the vanes 18. In theillustrated embodiment, the vanes 18 are substantially straight alongthe length of the vanes 18. However, in other embodiments for example,the vanes 18 can be bowed in either direction with respect to thedirection of rotation of the fan 50.

In some embodiments of the present invention, the orientation of theleading and trailing edges of the vanes can significantly influence theperformance of the fan assembly 10. With reference to FIG. 8, theorientation of the leading edge 30 of each vane 18 can be defined atleast in part by an angle D between a plane orthogonal to the axis ofrotation of the fan assembly 10 and a line tangent to the surface of thevane 18 facing (or at least partially facing) the fan blades 58 at theleading edge 30 of the vane 18. As discussed herein, the shape and/ororientation of the vanes 18 can change along the lengths of the vanes18. Accordingly, in some embodiments, this leading edge or “inlet” angleD is measured at a mid-point along the lengths of the vanes 18, or at(½R) or (⅔R) in other embodiments (where R is the radius of the fanassembly 10 at the outer limits of the vanes 18).

Iri some embodiments, this leading edge or “inlet” angle D of the vanes18 is at least 20° and/or is no greater than 70°. Better performanceresults can be achieved by employing an angle D that is at least 30°and/or is no greater than 60°. Still better performance can be achievedby employing an angle D that is at least 45° and/or is no greater than55°. These ranges are generally applicable to fans having a nominal sizefrom about six inches to about eighteen inches, although such vane inletangles D can be employed in fan assemblies having any diameter.Depending upon other parameters on the fan assembly 10, such as the typeand characteristics of the fluid being moved, the normal operationalspeed (or anticipated ranges of speeds) of the fan assembly 10, and thelike, the vane inlet angle D can vary.

In some embodiments of the present invention, the vane inlet angles (orranges of vane inlet angles) described above are employed alone or incombination with other characteristics of the fan assembly 10 describedherein to generate superior fan performance. With continued reference toFIG. 8, the orientation of the trailing edge 34 of each vane 18 can bedefined at least in part by an angle E between a plane parallel to andpassing through the axis of rotation of the fan assembly 10 and a linetangent to the surface of the vane 18 facing (or at least partiallyfacing) the fan blades 58 at the trailing edge 34 of the vane 18. Asdiscussed herein, the shape and/or orientation of the vanes 18 canchange along the lengths of the vanes 18. Accordingly, in someembodiments, this trailing edge or “outlet” angle E is measured at amid-point along the lengths of the vanes 18, or at (½R) or (⅔R) in otherembodiments (where R is the radius of the fan assembly 10 at the outerlimits of the vanes 18).

In some embodiments, this trailing edge or “outlet” angle E of the vanes18 is at least −30° and/or is no greater than 30° (wherein a negativeangle refers to an angle in a direction opposite the direction ofrotation of the fan 50 as viewed in FIG. 8, and wherein a positive anglerefers to an angle in the direction of rotation of the fan 50 as alsoviewed in FIG. 8). However, an angle E of at least −10° and/or nogreater than 20° can provide better performance results. Also, an angleE of at least −5° and/or no greater than 10° can provide still betterfan performance. These ranges are generally applicable to fans having anominal size from about six inches to about eighteen inches, althoughsuch vane outlet angles E can be employed in fan assemblies having anydiameter. Depending upon other parameters on the fan assembly 10, suchas the type and characteristics of the fluid being moved, the normaloperational speed (or anticipated ranges of speeds) of the fan assembly10, and the like, the vane outlet angle E can vary.

In some embodiments of the present invention, the vane outlet angles (orranges of vane outlet angles) described above are employed alone or incombination with other characteristics of the fan assembly 10 describedherein to generate superior fan performance.

In some embodiments of the present invention, selected rearwardly-sweptangles or ranges of angles of the vanes 18 (when viewed along the axisof rotation of the fan assembly 10) are employed alone or in combinationwith other characteristics of the fan assembly 10 described herein togenerate superior fan performance. A vane 18 is said to berearwardly-swept when a radially outermost end of the vane 18 is locatedcircumferentially behind a radially innermost end with reference to thedirection of rotation of the fan 50. A rearwardly-swept vane 18 can bedefined by an angle between a line extending along the leading ortrailing edge 34, 30 of the vane 18 and a straight line extending fromthe axis of rotation of the fan assembly 10 through a radially innermostpoint on the vane 18. In other embodiments (such as those embodiments inwhich the vane 18 is not straight along the length of the vane 18), theamount which a vane 18 is rearwardly-swept can be defined by an anglebetween the chord of the vane 18 (or, if no chord can be readilyidentified, a straight line extending through the radially innermost andoutermost points of the vane 18) and a straight line extending from theaxis of rotation of the fan assembly 10 through the radially innermostpoint of the vane 18. All measurements of the angle defining therearward sweep of the vane 18 (referenced herein and in the appendedclaims) are made with reference to a plan view of the fan assembly 10such as that shown in FIGS. 4 and 6.

In some embodiments of the present invention, this rearward sweep angleof the vanes 18 is no less than 5° and/or is no greater than 45°.However, better performance results can be achieved by employing arearward sweep angle that is less than 10° and/or is no greater than35°. Also, a rearward sweep angle that is less than 10° and/or is nogreater than 25° can produce still better fan performance. These rangesare generally applicable to fans having a nominal size from about sixinches to about eighteen inches. However, these ranges are not limitedto fans of such size. Depending upon other parameters on the fanassembly 10, such as the type and characteristics of the fluid beingmoved, the normal operational speed (or anticipated ranges of speeds) ofthe fan 50, and the like, this angle can vary.

As illustrated in FIGS. 2-6, the vaned area of the shroud 14 can besplit into two radial areas—one area for radially outer vanes 22 and theother area for radially inner vanes 26. In some embodiments, dividingthe vaned area into two areas 22, 26 can improve performance of the fanassembly 10 and/or can provide greater structural strength to the shroud14. Since pressure gradients can occur across the length of the fanblades 58, in some cases the performance of the fan assembly 10 can beimproved by selecting the number of vanes 18 in both the outer 22 andinner 26 vane areas based upon desired operational characteristics ofthe fan assembly 10 (e.g., fan speed, fan power, and the like). Forexample, in the illustrated embodiment, thirty-seven outer vanes 22 andtwenty-one inner vanes 26 are used to achieve good fan performance undercertain conditions. However, in various other operating conditions(i.e., for different fan speeds and diameters, when moving differentfluids having different properties, for fans having different fan bladeshapes, and the like), the number of vane areas and the vane countwithin those areas can be altered as desired. For example, in someembodiments, the inner vanes 26 and the outer vanes 22 are integral. Inother words, the outer vanes 22 can extend all the way to the centralhub (if employed). Additionally, in yet other embodiments, the innervanes can be omitted, leaving a ring-shaped gap between a motor housingwall 53 (if employed) of the shroud 14 and the outermost tier of vanes22, in which case struts or other structural members can secure themotor housing wall 53 to the rest of the shroud 14. Furthermore, in someembodiments, additional tiers of vanes can be employed (i.e., inner,outer, and middle; first, second, third, etc.).

The vanes located in various tiers need not necessarily have the samecharacteristics as vanes located in other tiers. For example, the innervanes 26 in the illustrated embodiment can have the same or differentcross-sectional shapes as the outer vanes 22, and can have any shapedescribed above. By way of example only, the inner vanes 26 in theillustrated embodiment can have a first shape, while the outer vanes 22can have a second shape different from the first. Additionally, thedifferent tiers of vanes can be oriented in any manner described above.Thus, the inner vanes 26 can have first orientation, while the outervanes 22 can have a second orientation different than the first.

In some embodiments, the number of vanes in each tier can be the same.However, in other embodiments, the number of vanes in each tier can bedifferent. In some embodiments, the blade-to-vane count is about 10:50(e.g., in some 11-inch diameter fans according to the presentinvention). However, regardless of the number of vaned areas or tiersemployed (i.e., the number of areas of the shroud 14 having differentsets of vanes 18), it is desirable in some embodiments to employ anumber of vanes that is not a multiple of the blade count. When the vanecount is a multiple of the blade count, harmonics can be more likely todevelop, causing pressure problems within the fan 50 and resultingperformance reductions of the fan assembly 10. For example, if the fan50 were to have a blade count of ten blades 58, then in some embodimentsnone of the vanes areas (if there is more than one) would have a vanecount equal to a multiple of ten, such as twenty, thirty, forty, fifty,sixty, etc. In some embodiments, the blade-to-vane count is about 10:65(e.g., in some 12-inch diameter fans according to the presentinvention).

In some embodiments of the present invention, superior performanceresults can be obtained by employing a particular shroud solidity or byemploying any shroud solidity within a range of shroud solidities. Insuch embodiments, selected shroud solidities (or ranges of shroudsolidities) are employed alone or in combination with othercharacteristics of the fan assembly 10 described herein to generatesuperior fan performance. Shroud solidity is a characteristic of theoverall fan assembly 10 that can be selected to change the efficiency ofthe fan assembly 10. Referring to FIGS. 7 and 8, the solidity of theshroud is the ratio of a vane's chord length (indicated as “A”) to thegap (indicated as “B”) measured between the same point on two adjacentvanes. For example, in the illustrated embodiment, the measurement forshroud solidity is made from the midpoint of the trailing edge 34 of afirst vane 18 to the midpoint of the trailing edge 34 of an adjacentvane 18. In other embodiments, this measurement can be made at theleading edges 30 of the vanes 18 or anywhere between the leading andtrailing edges 30, 34 of the vanes 18. Note, however, that since thevanes 18 can be arranged in a radial fashion, the gap between vanes 18can vary along the radial length of the vanes 18. Thus, the measurementof shroud solidity as described above can vary along the vanes 18. Thechord length is measured along a line from the leading edge 30 to thetrailing edge 34 of the vane.

With continued reference to the measurement of shroud solidity describedabove, in some embodiments, the chord length of the vanes 18 is variablealong the length of the vane from root to tip. Thus, the chord length ofthe vanes 18 used to measure shroud solidity is measured at the samelocation used to measure the gap between adjacent vanes 18 as describedabove (both measurements being made at the same location anywhere alongthe length of the vanes 18). In the illustrated embodiment, for example,the gap and chord length measurements of the vanes 18 are taken at thesame point: at the midpoint of the outer vanes 22. In other words, theeither or both measurements can be taken at a radial mid-point in theouter two-thirds of the fan assembly 10. As discussed above, either orboth measurements can be taken elsewhere in other embodiments, such asanywhere along the outer vanes 22 in the illustrated exemplaryembodiment, at a location half way between the axis of rotation and theradially outermost ends of the vanes 18, at a location half way betweenthe radially innermost and radially outermost ends of the vanes 18, andthe like.

The solidity of the shroud 14 in some embodiments of the presentinvention is at least 0.2 and/or is no greater than 3.5 (e.g., measuredat the vane trailing edges and at a midpoint along the vanes of theshroud, such as at the midpoint of the outer vanes 22 in the illustratedembodiment).

However, a shroud solidity of at least 0.5 and/or no greater than 2.5can produce better performance results. Also, still better performanceresults can be achieved by employing a shroud solidity of at least 1.0and/or no greater than 2.0. These ranges are generally applicable tofans having a nominal size from about six inches to about eighteeninches. However, these ranges are not limited to fans of such size. Instill other embodiments of the present invention, the above-describedsolidity ranges are different, often depending at least in part uponother parameters on the fan assembly 10, such as the number of blades 58of the fan 50, the distance of the fan 50 from the shroud 14, the normaloperational speed (or anticipated ranges of speeds) of the fan 50, andthe like.

As shown in the illustrated exemplary embodiment, a motor 42 is used topower the fan assembly 10. The motor 42 of the fan assembly 10 can beany conventional motor 42, such as an AC or DC electric motor (by way ofexample only, a permanent split capacitor AC induction motor or abrushless DC motor). Some embodiments of the present invention utilize ahigh efficiency motor 42 to help reduce overall system inefficiencies.In some embodiments such as that shown in the figures, the motor 42 hasa motor housing 38 secured to the shroud 14. The motor 42 can instead beattached to the shroud 14 by one or more brackets connected to the motor42 and shroud 14, by mounting lugs on the motor 42 and/or shroud 14, andthe like. In the illustrated exemplary embodiment, the motor housing 38is attached to the shroud 14 through the use of conventional fasteners,such as screws, nuts and bolts, rivets, pins or other conventionalfasteners, by snap fit connections, adhesive or cohesive bondingmaterial, press fits, and the like.

With continued reference to the illustrated embodiment, the motor 42mounted on the shroud 14 has a drive shaft 46 that extends through themotor housing 38 to drive the fan 50. As shown in FIGS. 3 and 5, thedrive shaft 46 of the motor 42 can be attached to a hub 54 of the fan50. This attachment can be any conventional type of attachment, such asa keyed connection, a press or interference fit, a splined connection,or any other male/female connection (whether or not secured by a setscrew, pin, or other such element), a coupling connection, and the like.In those embodiments of the present invention in which the fan 50employs a hub 54, a plurality of fan blades 58 can be attached at thehub's periphery (or can be integral to the hub 54) and can extendradially outward therefrom. In other embodiments, the fan blades 58extend out from any other rotating central element to which the fanblades 58 are attached or with which the fan blades 58 are integral.Thus, rotation of the motor 42 causes the drive shaft 46 to rotate,which in turn causes the central hub 54 to rotate (if employed) andcauses the plurality of fan blades 58 to rotate.

In the illustrated embodiment of the present invention, the hub 54 has afirst face 55 that extends in a generally radial direction and which isgenerally perpendicular to the drive shaft 46. This first face 55 can becircular in shape with the drive shaft coupling to this facesubstantially at the center of the circle. In other embodiments, theportion to which the drive shaft 46 couples can have any shape desired,including without limitation a first face 55 that is concave or convexin the direction away from the fan assembly 10 (e.g., whether having arounded profile in either direction, a profile defined by planarsurfaces joined at angles with respect to one another, and the like). Inother embodiments, the forward end of the hub 54 is pointed or otherwiseprotrudes along the axis of rotation of the fan assembly 10. Other hubshapes 54 can be employed in still other embodiments of the presentinvention. With reference back to the illustrated exemplary embodiment,a second face 56 of the illustrated hub 54 extends from the periphery ofthe first face 55 towards the shroud 17, and can be joined directly tothe first face 55 or can be joined thereto by a curved or angledintermediate surface as shown in the figures. In the illustratedembodiment, this second face 56 wraps around and partially encloses aportion of the motor housing 38. As illustrated, the hub 54 incooperation with the shroud 14 can substantially enclose the motorhousing 38. In some embodiments, the motor 42 can be entirely enclosedor encased by the hub 54 and shroud 17 with the exception of a gapsufficient (or only sufficient) to provide rotational clearance betweenthe hub 54 and shroud 14.

The blades 58 of the fan 50 can be attached to or integral with the hub54 along the second surface 56 as shown in the figures. In otherembodiments, the blades extend from other portions of the hub determinedat least in part upon the shape of the hub 54 employed. Each blade 58has a root 62 and a tip 66. The blades 58 are coupled to or are integralwith the hub 54 at the root 62, with the remainder of the blade 58extending at least radially therefrom to the tip 66. The blades 58 canhave any shape desired, such as a cloverleaf, machete, or teardrop shapeby way of example only. In addition, the shape of the blades 58 canchange along their length (from root 62 to tip 66). By way of exampleonly, the shape of each blade 58 illustrated in the figures tapers fromroot 62 to tip 66. This tapered blade 58 can provide significantperformance enhancements to the fan assembly 10 of the presentinvention. In other embodiments, non-tapered blades 58 can instead beemployed.

The blades 58 can have any cross-sectional shape desired, includingwithout limitation rectangular, flat, triangular, irregular, and othercross-sectional shapes. In the illustrated embodiment for example, thefan blades 58 each have a generally airfoil-shaped cross-section as bestshown in FIG. 7. Referring to FIG. 7, the thicker portion of theillustrated airfoil (including the thick edge) is generally referred toas the leading edge 70 of the blade 58 because during normal rotation ofthe fan 50 it is rotationally ahead of the remainder of the blade 58.Conversely, the thinner portion of the blade (including the thin edge)is generally referred to as the trailing edge 74 because during normalrotation of the fan 50 it is rotationally behind the remainder of theblade 58. However, determination of the leading edge 70 and trailingedge 74 for a blade 58 is dependent upon the direction of rotation ofthe fan 50. Therefore, note that in the description which follows, termssuch as “forward,” “backward,” “leading” and “trailing” are all withrespect to the direction of rotation of the fan assembly 10 indicated inFIG. 6. It is apparent that if the fan 50 were to rotate in the oppositedirection, then these terms would be reversed (i.e., “forward” wouldbecome “backward” and “leading” would become “trailing”).

Referring to FIGS. 7 and 9, it is shown that the leading edge 70 of eachblade 58 is displaced axially with respect to the trailing edge 74. Thisis sometimes referred to as the pitch angle of the blade 58 or the angleof attack. With reference to the direction of airflow through the fanassembly 10 (in a generally axial direction) past the vanes 18 andblades 58, the leading edge 70 of each blade 58 is located upstream ofthe trailing edge 74, or is angled below a horizontal line drawn at thetrailing edge 74 of the blade 58 in FIG. 7 (wherein the blade 58 rotatesto the left in FIG. 7 in normal operation). Although each blade 58 caninstead be angled such that the leading edge 70 is instead locateddownstream of the trailing edge 74, or such that the leading andtrailing edges 70, 74 are at the same axial location in the fan assembly10, good performance results are achieved by the blades in which theleading edge 70 of each blade 58 is located upstream of the trailingedge 74. A pitch angle of at least 10 degrees and/or no greater than 35degrees at a midpoint along the length of each blade 58 can provide goodperformance results. However, a pitch angle of at least 12 degreesand/or no greater than 30 degrees at a midpoint along the length of eachblade 58 can provide better performance results. Also, a pitch angle ofat least 15 degrees and/or no greater than 23 degrees at a midpointalong the length of each blade 58 can provide still better performanceresults.

In some embodiments of the present invention, it is the angle of bladepitch that helps determine the amount of airflow and the pressuredifferential across the airfoil. In some embodiments, the pitch angle ofeach blade 58 varies radially. Stated another way, each blade's angle ofattack is different at the root 62 than it is at the tip 66. Thischaracteristic can be referred to as blade twist. In some embodiments ofthe present invention, selected blade twist angles (or ranges of bladetwist angles) are employed alone or in combination with othercharacteristics of the fan assembly 10 described herein to generatesuperior fan performance. FIG. 9 illustrates blade twist and aconvenient method of measuring the blade twist angle. To measure theblade twist angle as illustrated, a chord is drawn along the tip 66 ofthe blade 58 from the trailing edge 74 to the leading edge 70. Then, asecond chord is drawn at the root 62 of the blade 58 from the trailingedge 74 to the leading edge 70. The angle between the two chords is theblade twist angle. Any (or no) amount of blade twist can be employed inthe present invention. In some embodiments, a blade twist angle fallingbetween 0° and 45° can employed for good performance results. However, ablade twist angle falling between 5° and 25° can be employed for betterfan performance. Also, a blade twist angle falling between 8° and 18°can be employed for still better fan performance. Depending upon otherparameters on the fan assembly 10, such as the type and characteristicsof the fluid being moved, the normal operational speed (or anticipatedranges of speeds) of the fan 50, and the like, the blade twist angle canvary.

In some embodiments of the present invention, the fan blades 58 extendradially toward positions immediately adjacent the fan cylinder 17 ofthe shroud 14, wherein clearance exists (and in some cases, onlysufficient clearance exists) for rotation of the fan blades 58 withrespect to the shroud 14. The position of the fan blades 58 with regardto the shroud 14 can have an effect on the efficiency and performance ofthe fan assembly 10. For example, the clearance between the tips 66 ofthe blades 58 and the inside wall of the fan cylinder 17 as justdescribed can be an important parameter relating to the efficiency andperformance of the fan assembly 10. If close tip clearance is notmaintained, leakage can occur between the fan blade tips 66 and theshroud 14 because air will take the path of least resistance through thefan assembly 10, thereby generating reduced performance in regard topressure capabilities and airflow.

In some embodiments of the present invention, another parameter that caninfluence performance of the fan assembly 10 is the spacing between thevanes 18 on the shroud 14 and the blades 58 of the fan 50. In thoseembodiments in which the portions of the fan blades 58 and vanes 18closest to one another are the trailing edges 74 of the fan blades 58and the leading edges 30 of the vanes 18 (as discussed above), thisspacing is measured between the trailing edges 74 of the fan blades 58and the leading edges 30 of the vanes 18. However, in other embodimentsin which the pitch of the fan blades 58 is different and/or in which theorientation of the vanes 18 is different, this spacing is measuredbetween the closest portions of the fan blades 58 and vanes 18. In someembodiments of the present invention, selected vane-to-blade spacings(or ranges of vane-to-shroud spacings) are employed alone or incombination with other characteristics of the fan assembly 10 describedherein to generate superior fan performance. With reference to theillustrated exemplary embodiment, FIGS. 7 and 8 provide across-sectional view of the proximity of the fan blades 58 to the vanes18 on the shroud 14. In some embodiments, the gap between the trailingedges 74 of the fan blades 58 and the leading edges 30 of the vanes 18,as indicated by the letter C, is at least 0.15 inches and/or is nogreater than 1.5 inches. However, this gap can be at least 0.2 inchesand/or no greater than 1.0 inches for better performance results. Also,this gap can be at least 0.25 inches and/or no greater than 0.5 inchesfor still better fan performance. These ranges are generally applicableto fans having a nominal size from about six inches to about eighteeninches, although such gaps can be employed in fan assemblies having anydiameter. Depending upon other parameters on the fan assembly 10, suchas the type and characteristics of the fluid being moved, the normaloperational speed (or anticipated ranges of speeds) of the fan 50, andthe like, the gap between the fan blades 58 and the vanes 18 can vary.

In some embodiments of the present invention, significant performanceimprovements are achieved over conventional fan assemblies when one ormore of the fan assembly characteristics is employed as discussed above.By way of example only, the performance of the illustrated fan assembly10 having a nominal diameter of twelve inches is illustrated in FIGS.10A-10C and compared to two conventional twelve inch fans. The fanassembly 10 illustrated in the figures has a blade twist angle ofapproximately 11°, a solidity ratio of approximately 1.5 (measured at amid-point along the lengths of the outer vanes 22), a gap between bladetrailing edges 74 and vane leading edges of approximately 0.38 inches, avane inlet angle D of approximately 51° (measured at a mid-point alongthe lengths of the outer vanes 22), a vane outlet angle E ofapproximately 4° (measured at a mid-point along the lengths of the outervanes 22), a leading edge rearwardly-swept angle of approximately 16°and a blade pitch angle of approximately 19° (measured at a mid-pointalong the lengths of the outer vanes 22). The first conventional fanused to create the comparison in FIGS. 10A-10C is an twelve inch fancurrently available in the marketplace. This fan is labeled as Prior ArtFan No. 1 on FIGS. 10A-10C. The second conventional fan used in thecaparison is another twelve inch fan currently available in themarketplace. This fan is labeled as Prior Art Fan No. 2 on FIGS.10A-10C.

The characteristic curve plots in FIGS. 10A-10C illustrate the totalefficiency, the brake horsepower, and the static pressure of each fanassembly against air flow. These numbers were obtained experimentally bymeasuring and calculating the parameters at various air flows amounts.

The embodiments described above and illustrated in the figures arepresented by way of example only and are not intended as a limitationupon the concepts and principles of the present invention. As such, itwill be appreciated by one having ordinary skill in the art that variouschanges in the elements and their configuration and arrangement arepossible without departing from the spirit and scope of the presentinvention. For example, one or more of the above mentioned embodimentscan be applied to an axial fan individually or in combination toincrease the efficiency of the fan as desired.

1. A fan assembly, comprising: a motor; a fan rotatably coupled to themotor for rotation about an axis, the fan having a plurality of fanblades, each fan blade having a leading edge with respect to arotational direction of the fan blade and a trailing edge with respectto the rotational direction of the fan blade; and a shroud including aplurality of vanes extending transversely with respect to fluid flowthrough the fan assembly and through which fluid flows through the fanassembly, the vanes being located downstream of the fan and oriented toextend away from a central area of the shroud; each vane having: alength defined between a radially inner end of the vane and a radiallyouter end of the vane; a leading edge; a trailing edge downstream of theleading edge of the vane with respect to fluid flow through the fanassembly; and a rearward swept angle defined between a first straightline extending through the radially inner and outer ends of the vane anda second straight line extending from the axis of the fan to theradially inner end of the vane, wherein the rearward swept angle is noless than about 5 degrees and is no greater than about 45 degrees;wherein each of the vanes is spaced from an adjacent vane by a gapmeasured from a first point on a first vane to a corresponding point onan adjacent vane, each vane also having a chord length at the firstpoint measured from the vane leading edge to the vane trailing edge, thefan assembly having a ratio of chord length to vane gap of no less thanabout 0.2 and no greater than about 3.5.
 2. The fan assembly as claimedin claim 1, wherein the ratio of chord length to vane gap is no lessthan about 0.5 and is no greater than about 2.5.
 3. The fan assembly asclaimed in claim 1, wherein the ratio of chord length to vane gap is noless than about 1.0 and is no greater than about 2.0.
 4. The fanassembly as claimed in claim 1, wherein the rearward swept angle is noless than about 10 degrees and is no greater than about 35 degrees. 5.The fan assembly as claimed in claim 2, wherein the rearward swept angleis no less than about 10 degrees and is no greater than about 35degrees.
 6. The fan assembly as claimed in claim 3, wherein the rearwardswept angle is no less than about 10 degrees and is no greater thanabout 35 degrees.
 7. The fan assembly as claimed in claim 1, wherein therearward swept angle is no less than about 10 degrees and is no greaterthan about 25 degrees.
 8. The fan assembly as claimed in claim 2,wherein the rearward swept angle is no less than about 10 degrees and isno greater than about 25 degrees.
 9. The fan assembly as claimed inclaim 3, wherein the rearward swept angle is no less than about 10degrees and is no greater than about 25 degrees.
 10. The fan assembly asclaimed in claim 1, wherein: each vane has an inlet angle definedbetween a straight line tangent to the vane at the leading edge of thevane and a plane orthogonal to the axis of rotation of the fan; thestraight line lies in a plane tangent to an imaginary cylinder centeredat the axis of the fan; and the inlet angle is no less than about 20degrees and is no greater than about 70 degrees.
 11. The fan assembly asclaimed in claim 10, wherein the inlet angle is no less than about 30degrees and is no greater than about 60 degrees.
 12. The fan assembly asclaimed in claim 10, wherein the inlet angle is no less than about 45degrees and is no greater than about 55 degrees.
 13. The fan assembly asclaimed in claim 1, wherein: each vane has an outlet angle definedbetween a straight line tangent to the vane at the trailing edge of thevane and a line parallel to the axis of the fan; the straight line liesin a plane tangent to an imaginary cylinder centered at the axis of thefan; and the outlet angle is no less than about 30 degrees in adirection counter to rotation of the fan and is no greater than about 30degrees in a rotational direction of the fan.
 14. The fan assembly asclaimed in claim 13, wherein the outlet angle is no less than about 10degrees in a direction counter to rotation of the fan and is no greaterthan about 20 degrees in a rotational direction of the fan.
 15. The fanassembly as claimed in claim 13, wherein the outlet angle is no lessthan about 5 degrees in a direction counter to rotation of the fan andis no greater than about 10 degrees in a rotational direction of thefan.
 16. The fan assembly as claimed in claim 1, wherein the fan isseparated from the shroud by an axial gap between the leading edges ofthe vanes and the trailing edges of the fan blades, the gap being noless than about 0.15 inches and no greater than about 1.5 inches. 17.The fan assembly as claimed in claim 16, wherein the gap is no less thanabout 0.20 inches and is no greater than about 1.0 inches.
 18. The fanassembly as claimed in claim 16, wherein the gap is no less than about0.25 inches and is no greater than about 0.5 inches.
 19. The fanassembly as claimed in claim 1, wherein: each fan blade has a blade rootand a blade tip; each fan blade has a twisted shape along a length ofthe fan blade from the blade root to the blade tip, the twisted shapedefining a twist angle of the blade; and the blade twist angle is nogreater than about 45 degrees.
 20. The fan assembly as claimed in claim19, wherein the blade twist angle is no less than about 5 degrees and isno greater than about 25 degrees.
 21. The fan assembly as claimed inclaim 19, wherein the blade twist angle is no less than about 8 degreesand is no greater than about 18 degrees.
 22. The fan assembly as claimedin claim 1, wherein: each blade has a pitch angle with respect to aplane orthogonal to the axis of the fan; and the pitch angle is no lessthan about 10 degrees and is no greater than about 35 degrees.
 23. Thefan assembly as claimed in claim 22, wherein the pitch angle is no lessthan about 12 degrees and is no greater than about 30 degrees.
 24. Thefan assembly as claimed in claim 22, wherein the pitch angle is no lessthan about 15 degrees and is no greater than about 23 degrees.
 25. Thefan assembly as claimed in claim 1, wherein each of the vanes has anairfoil shaped cross section.
 26. The fan assembly as claimed in claim1, wherein each of the vanes has a cambered surface defining a curvedshape extending from the leading edge of the vane to the trailing edgeof the vane.
 27. A fan assembly, comprising: a motor; a fan rotatablycoupled to the motor for rotation about an axis, the fan having aplurality of fan blades, each fan blade having a leading edge withrespect to a rotational direction of the fan blade and a trailing edgewith respect to the rotational direction of the fan blade; and a shroudincluding a plurality of vanes extending transversely with respect tofluid flow through the fan assembly and through which fluid flowsthrough the fan assembly, the vanes being located downstream of the fanand oriented to extend away from a central area of the shroud; each vanehaving: a length defined between a radially inner end of the vane and aradially outer end of the vane; a leading edge; a trailing edgedownstream of the leading edge of the vane with respect to fluid flowthrough the fan assembly; and an inlet angle defined between a straightline tangent to the vane at the leading edge of the vane and a planeorthogonal to the axis of the fan, wherein the straight line lies in aplane tangent to an imaginary cylinder centered at the axis of the fan,the inlet angle being no less than about 20 degrees and is no greaterthan about 70 degrees; wherein each of the vanes is spaced from anadjacent vane by a gap measured from a first point on a first vane to acorresponding point on an adjacent vane, each vane also having a chordlength at the first point measured from the vane leading edge to thevane trailing edge, the fan assembly having a ratio of chord length tovane gap of no less than about 0.2 and no greater than about 3.5. 28.The fan assembly as claimed in claim 27, wherein the ratio of chordlength to vane gap is no less than about 0.5 and is no greater thanabout 2.5.
 29. The fan assembly as claimed in claim 27, wherein theratio of chord length to vane gap is no less than about 1.0 and is nogreater than about 2.0.
 30. The fan assembly as claimed in claim 27,wherein the inlet angle is no less than about 30 degrees and is nogreater than about 60 degrees.
 31. The fan assembly as claimed in claim28, wherein the inlet angle is no less than about 30 degrees and is nogreater than about 60 degrees.
 32. The fan assembly as claimed in claim29, wherein the inlet angle is no less than about 30 degrees and is nogreater than about 60 degrees.
 33. The fan assembly as claimed in claim27, wherein the inlet angle is no less than about 45 degrees and is nogreater than about 55 degrees.
 34. The fan assembly as claimed in claim28, wherein the inlet angle is no less than about 45 degrees and is nogreater than about 55 degrees.
 35. The fan assembly as claimed in claim29, wherein the inlet angle is no less than about 45 degrees and is nogreater than about 55 degrees.
 36. The fan assembly as claimed in claim27, wherein: each vane has an outlet angle defined between a straightline tangent to the vane at the trailing edge of the vane and a lineparallel to the axis of the fan; the straight line lies in a planetangent to an imaginary cylinder centered at the axis of the fan; andthe outlet angle is no less than about 30 degrees in a direction counterto rotation of the fan and is no greater than about 30 degrees in arotational direction of the fan.
 37. The fan assembly as claimed inclaim 36, wherein the outlet angle is no less than about 10 degrees in adirection counter to rotation of the fan and is no greater than about 20degrees in a rotational direction of the fan.
 38. The fan assembly asclaimed in claim 36, wherein the outlet angle is no less than about 5degrees in a direction counter to rotation of the fan and is no greaterthan about 10 degrees in a rotational direction of the fan.
 39. The fanassembly as claimed in claim 27, wherein the fan is separated from theshroud by an axial gap between the leading edges of the vanes and thetrailing edges of the fan blades, the gap being no less than about 0.15inches and no greater than about 1.5 inches.
 40. The fan assembly asclaimed in claim 39, wherein the gap is no less than about 0.20 inchesand is no greater than about 1.0 inches.
 41. The fan assembly as claimedin claim 39, wherein the gap is no less than about 0.25 inches and is nogreater than about 0.5 inches.
 42. The fan assembly as claimed in claim27, wherein: each fan blade has a blade root and a blade tip; each fanblade has a twisted shape along a length of the fan blade from the bladeroot to the blade tip, the twisted shape defining a twist angle of theblade; and the blade twist angle is no greater than about 45 degrees.43. The fan assembly as claimed in claim 42, wherein the blade twistangle is no less than about 5 degrees and is no greater than about 25degrees.
 44. The fan assembly as claimed in claim 42, wherein the bladetwist angle is no less than about 8 degrees and is no greater than about18 degrees.
 45. The fan assembly as claimed in claim 27, wherein: eachblade has a pitch angle with respect to a plane orthogonal to the axisof the fan; and the pitch angle is no less than about 10 degrees and isno greater than about 35 degrees.
 46. The fan assembly as claimed inclaim 45, wherein the pitch angle is no less than about 12 degrees andis no greater than about 30 degrees.
 47. The fan assembly as claimed inclaim 45, wherein the pitch angle is no less than about 15 degrees andis no greater than about 23 degrees.
 48. The fan assembly as claimed inclaim 27, wherein each of the vanes has an airfoil shaped cross section.49. The fan assembly as claimed in claim 27, wherein each of the vaneshas a cambered surface defining a curved shape extending from theleading edge of the vane to the trailing edge of the vane.
 50. A fanassembly, comprising: a motor; a fan rotatably coupled to the motor forrotation about an axis, the fan having a plurality of fan blades, eachfan blade having a leading edge with respect to a rotational directionof the fan blade and a trailing edge with respect to the rotationaldirection of the fan blade; and a shroud including a plurality of vanesextending transversely with respect to fluid flow through the fanassembly and through which fluid flows through the fan assembly, thevanes being located downstream of the fan and oriented to extend awayfrom a central area of the shroud; each vane having: a length definedbetween a radially inner end of the vane and a radially outer end of thevane; a leading edge; a trailing edge downstream of the leading edge ofthe vane with respect to fluid flow through the fan assembly; and anoutlet angle defined between a straight line tangent to the vane at thetrailing edge of the vane and a line parallel to the axis of the fan,wherein the straight line lies in a plane tangent to an imaginarycylinder centered at the axis of the fan; the outlet angle being no lessthan about 30 degrees in a direction counter to rotation of the fan andis no greater than about 30 degrees in a rotational direction of thefan; wherein each of the vanes is spaced from an adjacent vane by a gapmeasured from a first point on a first vane to a corresponding point onan adjacent vane, each vane also having a chord length at the firstpoint measured from the vane leading edge to the vane trailing edge, thefan assembly having a ratio of chord length to vane gap of no less thanabout 0.2 and no greater than about 3.5.
 51. The fan assembly as claimedin claim 50, wherein the ratio of chord length to vane gap is no lessthan about 0.5 and is no greater than about 2.5.
 52. The fan assembly asclaimed in claim 50, wherein the ratio of chord length to vane gap is noless than about 1.0 and is no greater than about 2.0.
 53. The fanassembly as claimed in claim 50, wherein the outlet angle is no lessthan about 10 degrees in a direction counter to rotation of the fan andis no greater than about 20 degrees in a rotational direction of thefan.
 54. The fan assembly as claimed in claim 51, wherein the outletangle is no less than about 10 degrees in a direction counter torotation of the fan and is no greater than about 20 degrees in arotational direction of the fan.
 55. The fan assembly as claimed inclaim 52, wherein the outlet angle is no less than about 10 degrees in adirection counter to rotation of the fan and is no greater than about 20degrees in a rotational direction of the fan.
 56. The fan assembly asclaimed in claim 50, wherein the outlet angle is no less than about 5degrees in a direction counter to rotation of the fan and is no greaterthan about 10 degrees in a rotational direction of the fan.
 57. The fanassembly as claimed in claim 51, wherein the outlet angle is no lessthan about 5 degrees in a direction counter to rotation of the fan andis no greater than about 10 degrees in a rotational direction of thefan.
 58. The fan assembly as claimed in claim 52, wherein the outletangle is no less than about 5 degrees in a direction counter to rotationof the fan and is no greater than about 10 degrees in a rotationaldirection of the fan.
 59. The fan assembly as claimed in claim 50,wherein the fan is separated from the shroud by an axial gap between theleading edges of the vanes and the trailing edges of the fan blades, thegap being no less than about 0.15 inches and no greater than about 1.5inches.
 60. The fan assembly as claimed in claim 59, wherein the gap isno less than about 0.20 inches and is no greater than about 1.0 inches.61. The fan assembly as claimed in claim 59, wherein the gap is no lessthan about 0.25 inches and is no greater than about 0.5 inches.
 62. Thefan assembly as claimed in claim 50, wherein: each fan blade has a bladeroot and a blade tip; each fan blade has a twisted shape along a lengthof the fan blade from the blade root to the blade tip, the twisted shapedefining a twist angle of the blade; and the blade twist angle is nogreater than about 45 degrees.
 63. The fan assembly as claimed in claim62, wherein the blade twist angle is no less than about 5 degrees and isno greater than about 25 degrees.
 64. The fan assembly as claimed inclaim 62, wherein the blade twist angle is no less than about 8 degreesand is no greater than about 18 degrees.
 65. The fan assembly as claimedin claim 50, wherein: each blade has a pitch angle with respect to aplane orthogonal to the axis of the fan; and the pitch angle is no lessthan about 10 degrees and is no greater than about 35 degrees.
 66. Thefan assembly as claimed in claim 65, wherein the pitch angle is no lessthan about 12 degrees and is no greater than about 30 degrees.
 67. Thefan assembly as claimed in claim 65, wherein the pitch angle is no lessthan about 15 degrees and is no greater than about 23 degrees.
 68. Thefan assembly as claimed in claim 50, wherein each of the vanes has anairfoil shaped cross section.
 69. The fan assembly as claimed in claim50, wherein each of the vanes has a cambered surface defining a curvedshape extending from the leading edge of the vane to the trailing edgeof the vane.
 70. A fan assembly, comprising: a motor; a fan rotatablycoupled to the motor for rotation about an axis, the fan having aplurality of fan blades, each fan blade having a leading edge withrespect to a rotational direction of the fan blade and a trailing edgewith respect to the rotational direction of the fan blade; and a shroudincluding a plurality of vanes extending transversely with respect tofluid flow through the fan assembly and through which fluid flowsthrough the fan assembly, the vanes being located downstream of the fanand oriented to extend away from a central area of the shroud; each vanehaving: a length defined between a radially inner end of the vane and aradially outer end of the vane; a leading edge; and a trailing edgedownstream of the leading edge of the vane with respect to fluid flowthrough the fan assembly, wherein the shroud is separated from the fanby an axial gap between the leading edges of the vanes and the trailingedges of the fan blades, the gap being no less than about 0.15 inchesand no greater than about 1.5 inches; wherein each of the vanes isspaced from an adjacent vane by a gap measured from a first point on afirst vane to a corresponding point on an adjacent vane, each vane alsohaving a chord length at the first point measured from the vane leadingedge to the vane trailing edge, the fan assembly having a ratio of chordlength to vane gap of no less than about 0.2 and no greater than about3.5.
 71. The fan assembly as claimed in claim 70, wherein the ratio ofchord length to vane gap is no less than about 0.5 and is no greaterthan about 2.5.
 72. The fan assembly as claimed in claim 70, wherein theratio of chord length to vane gap is no less than about 1.0 and is nogreater than about 2.0.
 73. The fan assembly as claimed in claim 70,wherein the gap is no less than about 0.20 inches and is no greater thanabout 1.0 inches.
 74. The fan assembly as claimed in claim 71, whereinthe gap is no less than about 0.20 inches and is no greater than about1.0 inches.
 75. The fan assembly as claimed in claim 72, wherein the gapis no less than about 0.20 inches and is no greater than about 1.0inches.
 76. The fan assembly as claimed in claim 70, wherein the gap isno less than about 0.25 inches and is no greater than about 0.5 inches.77. The fan assembly as claimed in claim 71, wherein the gap is no lessthan about 0.25 inches and is no greater than about 0.5 inches.
 78. Thefan assembly as claimed in claim 72, wherein the gap is no less thanabout 0.25 inches and is no greater than about 0.5 inches.
 79. A fanassembly, comprising: a motor; a fan rotatably coupled to the motor forrotation about an axis, the fan having a plurality of fan blades, eachfan blade having a leading edge with respect to a rotational directionof the fan blade and a trailing edge with respect to the rotationaldirection of the fan blade; and a shroud including a plurality of vanesextending transversely with respect to fluid flow through the fanassembly and through which fluid flows through the fan assembly, thevanes being located downstream of the fan and oriented to extend awayfrom a central area of the shroud, each vane having a leading edge and atrailing edge downstream of the leading edge with respect to fluid flowthrough the fan assembly, each of the vanes spaced from an adjacent vaneby a gap measured from a first point on a first vane to a correspondingpoint on an adjacent vane, each vane also having a chord length at thefirst point measured from the vane leading edge to the vane trailingedge, the fan assembly having a ratio of chord length to vane gap of noless than about 0.2 and no greater than about 2.5.
 80. The fan assemblyas claimed in claim 79, wherein the ratio of chord length to vane gap isno less than about 0.5 and is no greater than about 2.5.
 81. The fanassembly as claimed in claim 79, wherein the ratio of chord length tovane gap is no less than about 1.0 and is no greater than about 2.0.